Why don't u do it "semi-automatic"? Increase clocks in 5-10mhz steps, look for artifakts & temps and be carefull! I know I would. In settings, sec or third "page" set the artifact scanning.
But why do you push it? Isn't that the beast allready

I have kind of same problem with my Sapphire X1950XT. I use ATI Tools 0.26 and when i try to find the max core or max mem freq the freq goes up with out find any artis til the system hungs up or restart... WTF is happening??? Shouldnt ATI Tools report artis before crashing up the system???

yeah ... i am having similar problem with 7900gs.. artifacts remaining undetected even when moved the slieder for detectection to max "sensitivity"...
i thing there is generally something wrong with artefact detection of ati tool 0.26